1. Field of the Invention
This invention relates generally to external combustion expander-type engines. More particularly, the present invention relates to an external combustion expander-type engine having an expansion chamber between the combustion chamber and hot gas distributor rotary valve.
2. Description of the Art
It is known to propel a torpedo with a propulsion system which uses an external combustion expander-type engine in conjunction with a monopropellant fuel. A monopropellant fuel contains the chemical species necessary for its own combustion or decomposition. A common monopropellant fuel used in United States Navy torpedoes is designated OTTO Fuel II, which uses a nitrated alcohol as its energetic constituent. Otto Fuel II is a mixture of 76% propylene glycol dinitrate, 1.5% 2-Nitrodiphenylamine and 22.5% Di-n-butyl sebacate (by weight). The decomposition of OTTO Fuel II yields approximately 1,100 btu per pound (11,275 btu/gal) at a flame temperature of approximately 2,300.degree. F.
In a conventional propulsion system of this type, a solid propellant initiator charge is first fired into the combustion chamber, producing a hot, energized gas which commences drive action of the torpedo and initiates the entry of a liquid sustainer monopropellant fuel (e.g., OTTO Fuel II) into the combustion chamber through a poppet valve. Heat generated in the combustion of the initiator propellant effects combustion of the initial quantity of sustainer propellant which is admitted to the combustion chamber. Subsequently, combustion of the sustainer fuel continues in a self-sustaining manner due to the high temperature in the chamber, i.e., part of the energy generated in combustion of the sustainer propellant is used to combust additional sustainer propellant.
Combustion of OTTO Fuel II produces a variety of toxic or otherwise harmful emissions. It is also corrosive to torpedo hardware. A number of known fuels represent potential alternative monopropellants. These include combinations of hydroxylammonium nitrate (HAN) or hydroxylammonium perchlorate (HAP)--both oxidizers--with various fuels such as triethanolammonium nitrate (TEAN). Such fuels may be diluted with deionized water to reduce decomposition/combustion temperatures to the 2300.degree. F. requirement of existing torpedo hardware.